Effect of Heat Treatment on Acoustic Properties of Chromium Polycrystals at Low Temperatures

Abstract

Acoustic properties of polycrystalline Cr samples of 99.99 % purity are investigated at frequencies of longitudinal vibrations f ~ 75 kHz and of bending vibrations at 0.6 < f < 1.5 kHz when thermocycling within the temperature interval 5 − 330 K. Special attention is paid to the acoustic anomalies in the vicinity of the magnetic phase transitions: the Néel point and the spin-flip transition. In the as-received samples, a significant hysteresis of the acoustic properties has been found for the first time. The effect of heat treatments on internal friction and elastic properties of chromium polycrystals is also investigated. The data obtained are compared with the effect of small preliminary deformation and а long-time ageing at room temperature on the ultrasound anomalies in Cr single crystal. The observed behavior of the acoustic properties may be caused by changes in the antiferromagnetic domain structure in Cr polycrystals under the action of thermoelastic stresses arising from quenching, preliminary plastic deformation or thermocycling.